1. Field
The present invention relates generally to communications, and more specifically to distributed hierarchical scheduling in an ad hoc network.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice and data. A typical wireless data system, or network, provides multiple users access to one or more shared resources. A system may use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), and others.
Example wireless networks include cellular-based data systems. The following are several such examples: (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard), and (4) the high data rate (HDR) system that conforms to the TIA/EIA/IS-856 standard (the IS-856 standard).
Other examples of wireless systems include Wireless Local Area Networks (WLANs) such as described in the IEEE 802.11 standards (e.g. 802.11(a), (b), or (g)). Improvements over these networks may be achieved in deploying a Multiple Input Multiple Output (MIMO) WLAN comprising Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques.
WLANs are commonly deployed to provide data services to one or more user terminals within an area. A cellular-like deployment of WLAN coverage areas may be deployed with an access point providing coverage for each cell. This nominal cellular architecture assumes that each access point has wired backhaul connectivity (e.g. a T1 backhaul). For example, 802.11 hotspots with a T1 backhaul are commonly deployed in various locations to provide access. A typical cellular-like WLAN deployment is illustrated in FIG. 1. In this example, data links 110A-C connect Internet 102 with Access Points (APs) 104A-C. Each access point 104 has a coverage area, commonly referred to as a cell 130, in which various User Terminals (UTs) 106 may communicate with the access point 104 via a wireless link 120.
Due to the limited cell radius and dense deployment of APs, as well as the expense, limited bandwidth and limited availability of T1 backhaul, alternate methods of backhaul are of interest. Various ad hoc networks may be formed. For example, consider a multi-hop wireless backhaul architecture, where APs form a peer-to-peer mesh network. In such a hierarchical architecture, only the APs, and not the user terminals (UTs) supported by each AP, participate in the backbone mesh. An earlier, similar approach is the Ricochet model, developed by Metricom Inc., of San Jose, Calif., now owned by YDI Wireless, Inc., of Falls Church, Va. In order to enable a mesh network, protocols are needed to establish communication between nodes in the mesh, also needed are techniques for scheduling reception and transmission to maximize throughput and/or minimize interference between mesh nodes and/or user terminals communicating via the mesh network. There is therefore a need in the art for distributed hierarchical scheduling in an ad hoc network.